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1、A NEMA Lighting Systems Division Document LSD 46-2009 Photoluminescent Exit SignageFactual Review Prepared by Emergency Lighting Section National Electrical Manufacturers Association 1300 North 17th Street, Suite 1752 Rosslyn, Virginia 22209 The requirements or guidelines presented in this document,
2、 a NEMA Lighting Systems Division white paper, are considered technically sound at the time they are approved for publication. They are not a substitute for a product sellers or users own judgment with respect to the particular product discussed, and NEMA does not undertake to guarantee the performa
3、nce of any individual manufacturers products by virtue of this document or guide. Thus, NEMA expressly disclaims any responsibility for damages arising from the use, application, or reliance by others on the information contained in these white papers, standards, or guidelines. LSD 46-2009 Contents
4、1 Introduction3 2 Safety.3 3 Energy Consumption .6 4 Total Cost.7 5 Enforceability in the Field.8 6 Conclusion.8 Copyright 2009 by the National Electrical Manufacturers Association. 2 LSD 46-2009 1 Introduction Most would agree the use of low-path egress markings using photoluminescent material adds
5、 to the safe evacuation of any building during an emergency evacuation under power failure conditions. This technology has distinct advantages in numerous applications where traditional egress marking equipment is not an ideal solution. The purpose of the following text is to clarify misunderstandin
6、gs that might ensue from potentially erroneous claims concerning this type of product. Specifically targeted are claims such as “no electricity consumption,” “no maintenance,” “exit signs illuminate for hours without charging” or that the signs are “always ready.” This paper will briefly examine som
7、e key facts about exit signage in the areas of safety, energy consumption, installation and maintenance costs, and enforceability in the field, so that potentially erroneous claims may be evaluated. 2 Safety Some have claimed that photoluminescent exit signs are the best solution to life safety requ
8、irements because they can offer several hours of “glowing” in total darkness while consuming zero energy during their “charge state” and useful life. While it is true that good quality photoluminescent signs will continue to emit some light for a period of time, the luminance of these signs will dec
9、ay rapidly with time. This luminance decay characteristic, described below, must be factored into the decision of whether this technology is suitable for a particular application. Photoluminescent exit signs can be significantly dimmer than internally illuminated signs. After full exposure to extern
10、al lighting, the initial light emission (luminance) of these exit signs typically averages only 12% of the minimum required by UL standards for internally illuminated signs, that is, 1 Cd/m2 (1 lux) compared to 8.5 Cd/m2 (8.5 lux). Based on data gathered from manufacturer websites after 10 minutes o
11、f glowing in the dark, typical photoluminescent exit signs have lost up to 80% of their original intensity and show an average luminance of only 0.1-0.06 Cd/m2. After 60 minutes, the average luminance falls to roughly 0.03-0.01 Cd/m2). After 90 minutes, it dips to 0.02-0.01 Cd/m2, depending on the q
12、uality or density of the photoluminescent pigments. In reality, photoluminescent material loses its discernability against other signs if ambient light is above 2 or 3 lux. 1 1 For an illustration of manufacturer claims, see the PNA Groups industry support letter, found at http:/ It should be noted
13、that on page 3 paragraph 2, there is a decimal (units) error regarding Internally Illuminated LED Exit Signage. In accordance with UL 924 section 41.3.5, the requirement for internally lit signage is 8.5 Cd/m2; that is, 8.5 candelas (cd) per square meter, not millicandelas (mcd) as written in the do
14、cument. To compare photoluminescent signage performance against internally lit signage, one should ensure the same units of expression before making a judgment. Copyright 2009 by the National Electrical Manufacturers Association. 3 ? LSD 46-2009 Photoluminescent Exit Sign Lux from 0-90 Minutes (Star
15、ting at one (1) Lux at Time = 0) 0 0.05 0.1 0.15 0.2 0.25 0306090 Time (m) Lux (Cd/m2) High Low Figure 1: Graph Illustrating Typical Photoluminescent Sign Lux Values During Discharge There are two test methods for evaluating exit signs for compliance to the UL 924 standard for emergency lighting and
16、 power equipment. The first test is an objective test based on the analytical luminance measurements of the sign. Signs tested in accordance with this method must meet minimum luminance levels under normal conditions during a black out and at the end of the rated time (never less than 90 minutes). C
17、onditions Minimum Luminance Normal conditions 8.57cd/m2 2 End of rated time (90 minutes) 5.14cd/m2 3 The test requires the use of test instruments that are calibrated and traceable to NIST standards, and describes clearly: - the minimum value of luminance (brightness) of any point on the legend - av
18、erage luminance of the legend - luminance uniformity, etc. - test results can easily be reproduced and verified. The second test method is the Observation Visibility test and can be used to certify exit signs if the signs do not meet the minimum luminance requirements. 2 This threshold is based on a
19、 study by M. J. Ouellette: Visibility of Exit signs under National Research Council of Canada, as optimum visibility during day, night, and smoke conditions 3 Emergency Lighting and Power EquipmentUL 924, section 41.3.5 Copyright 2009 by the National Electrical Manufacturers Association. 4 ? LSD 46-
20、2009 The Observation Visibility test consists of selecting observers from certain age groups (1830, 3140, 4150, and 5170 years old) who have been determined to be in good health (i.e., corrected vision). After the sign has been kept in total darkness for 90 minutes and after allowing each observer f
21、ive minutes to acclimate his or her eyes to the ambient light conditions, a subjective test is conducted (no instruments of measure are used). - Some signs are modified, showing, for example, an F instead of the E.4 - Witnesses are asked to look at the signs and see if these show the correct spellin
22、g of the legend. - The sign is considered visible enough if the average (mean) of correct readings is 80% or greater5. If the average works out to be less than 80%, a further allowance using statistical analysis allows wide variations to be eliminated and a new average calculated. If the adjusted av
23、erage meets the 80% minimum, the sign is once again found to be acceptable. The human eye can adapt in the dark to extremely low luminance levels after a certain adjustment period. The visual testing of exit signs includes a five minute period for observers eyes to adapt to the dark. This is somethi
24、ng that would not typically be afforded in an emergency situation: wasting the first five minutes of the time allotted for egress waiting for the eye to acclimate to the dark environment. The visual testing method is not only costly and difficult to execute in a laboratory setting, but also discoura
25、ges attempts by third parties to validate or benchmark6 compliance. A few questions that arise from the Observation Visibility test: - How long can we afford to wait in the dark during an emergency evacuation for our eyes to adjust? - How “low/dim” can we afford an exit sign to be when were looking
26、for the way out? - How visible do exit signs have to be for people of various ages and states of health to be able to read them, and should/could they be less visible than todays standards? In addition to the test program parameters mentioned above, there are also categorical listings to consider th
27、at establish another set of installation and performance requirements. Upon UL qualification of materials and product, and based on the products use in real life, a Category Control Number, or CCN, is issued. The CCN establishes the “conditions of acceptability,” if you will, to provide the details
28、required for 4 In doubt, the witness therefore has a 50% chance of guessing the correct answer 5 ISO 3864 international standard for safety symbols targets 95% of the people can detect the sign 6 The impracticality of benchmarking happens when so much effort and energy are exerted to apply ISO 17025
29、, which imposes the evaluation of extremely precise uncertainty criteria, further complicating the evaluation of conformity Copyright 2009 by the National Electrical Manufacturers Association. 5 ? LSD 46-2009 proper use in accordance with the product listing. The three CCN profiles derived from UL s
30、tandard 924 are: ! FTBREmergency lighting and power equipment ! FWBOExit signs ! FWBXExit signs, self-luminous and Photoluminescent Internally illuminated exit signs are covered under FTBR and FWBO while photoluminescent signs are covered under FWBX. The guide information found in FWBX illustrates t
31、he viewing distance limitation placed on numerous photoluminescent signs being 50 or 75 feet maximum while a few products bear a 100 feet maximum viewing distance. Where design professionals default the placement of exit signs, in accordance with the IBC, NEC, and NFPA 101 at 100 feet maximum, witho
32、ut consideration of performance differences, it could potentially result in non-compliant photoluminescent exit sign installations. Additionally, this may also result in non- compliance if a property or facility owner opts to replace an existing internally illuminated sign with a photoluminescent pr
33、oduct. UL category FWBX further requires 5 fc of illumination on the face of the sign for proper operation; this is in direct conflict with claims that photoluminescent exit sign technologies effectively operate with zero power consumed. 3 Energy Consumption There is a belief that photoluminescent e
34、xit signs consume no electrical energy, since they can charge from the ambient, normal lighting. This is NOT always the case. Some codes require these exits to be continuously illuminated while the building is occupied as this is the only way to ensure the photoluminescent material will be fully cha
35、rged if an emergency or loss of power occurs. Additionally, both the International Building Code (IBC) and NFPA 101, Life Safety Code (LSC) indicate that exit signs shall be illuminated at all times or that photoluminescent signage should be illuminated at least 60 minutes prior to occupancy. How a
36、building manager might correctly and safely determine for all possible cases when 60 minutes prior to occupancy occurs so as to have the charging lighting for the photoluminescent signage turn on is a distinct challenge. Automatic timers cannot take into account unscheduled or early arrivals. As man
37、y building managers are turning towards occupancy sensors and dimming solutions, photoluminescent signage could not safely rely upon ambient lighting in these situations and so dedicated lighting for photoluminescent sign charging might have to be added. Internally illuminated signs consume electric
38、ity 24 hours a day. However, these signs, by law, must consume no more than 5 watts per face (EPAct 2005), and the reality is that most internally illuminated signs consume less than 2 watts per face. Photoluminescent exit signs, on the other hand, call for far more electrical consumption to be kept
39、 properly charged. Specifications printed on the frame of the exit sign state “a Copyright 2009 by the National Electrical Manufacturers Association. 6 ? LSD 46-2009 minimum 5 fc (54 lux) externalillumination must be present at all times during building occupancy.” The standard for performance evalu
40、ation of photoluminescent exit signs (UL 924) also requires the light source for exposure to be of a type that will give adequate UV levels to properly recharge the sign. These lamps should be considered part of the exit signage system when using a photoluminescent exit sign. A building owner theref
41、ore might easily experience a higher cost to maintain and operate correctly installed photoluminescent exits signs as compared to internally lit signage. 4 Total Cost The total cost of an exit sign system includes several components: cost of the equipment, installation, maintenance, and energy consu
42、mption. Installation There is a belief that photoluminescent exit signs cost much less to install, as it is likened to “hanging a framed picture on the wall.” This is NOT the case with emergency lighting. As mentioned in Section 3, there are situations where code requires these panels to be continuo
43、usly illuminated, or at the very least when the building is occupied, if not 60 minutes before. This means the lamp used to illuminate a photoluminescent sign must in some cases be on at all times and that it cannot be on any switching, dimming, or sensor systems. Hence, the correct installation of
44、a photoluminescent exit sign will include special, dedicated electrical wiring. In addition, the installation requires an installer to use a light meter to verify the illumination level to ensure it is in accordance with the code and product listing and meets the 54 lux level. Maintenance Apart from
45、 the standard periodic inspections and cleaning (dusting), photoluminescent signs will also lead to frequent re-lamping of failed incandescent or fluorescent lamps used for their illumination. Because of its limited discernability, layout re-arrangement, including lighting, deserves the same attenti
46、on. As facility owners may not have the in- depth level of understanding of the code requirement for constant illumination of 5 fc on the face, improper re-lamping may result in product that is left without adequate charging for long periods of time, resulting in non-compliant life safety product. T
47、he average life of an incandescent lamp is around 750 hours7 (31.25 days). A linear fluorescent might last 20,000 hours (2.3 years). By comparison, most internally lit exit sign manufacturers can offer LED strips that will maintain their light level for at least 10 years. 7 http:/www.eia.doe.gov/eme
48、u/lighting/chap3.html Copyright 2009 by the National Electrical Manufacturers Association. 7 ? LSD 46-2009 Energy As stated previously, major code authorities, being more concerned about evacuation, indicate that exit signs need to be illuminated at all times. This being true for photoluminescent ex
49、it signs establishes the need for dedicated, continuously maintained lighting. This negates claims that photoluminescent exit signs may safely rely on ambient lighting. As described above, there must be dedicated lighting, typically consuming 3460 watts of power. This is at least ten times more than the 35 watts of power required to maintain compliant LED exit signs. However, this power consumption impact could be reduced through properly combin